linux-kernel - Re: [PATCH] iommu: fix return error code in iommu_probe

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Date:   Thu, 26 Nov 2020 08:59:08 +0000
From:   Will Deacon <will@...nel.org>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: fix return error code in iommu_probe_device()

On Thu, Nov 26, 2020 at 10:29:57AM +0800, Yang Yingliang wrote:
> 
> On 2020/11/25 19:35, Will Deacon wrote:
> > On Wed, Nov 25, 2020 at 09:54:34AM +0800, Yang Yingliang wrote:
> > > On 2020/11/18 6:41, Will Deacon wrote:
> > > > On Tue, Nov 17, 2020 at 07:11:28PM +0800, Yang Yingliang wrote:
> > > > > On 2020/11/17 17:40, Lu Baolu wrote:
> > > > > > On 2020/11/17 10:52, Yang Yingliang wrote:
> > > > > > > If iommu_group_get() failed, it need return error code
> > > > > > > in iommu_probe_device().
> > > > > > > 
> > > > > > > Fixes: cf193888bfbd ("iommu: Move new probe_device path...")
> > > > > > > Reported-by: Hulk Robot <hulkci@...wei.com>
> > > > > > > Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> > > > > > > ---
> > > > > > >     drivers/iommu/iommu.c | 4 +++-
> > > > > > >     1 file changed, 3 insertions(+), 1 deletion(-)
> > > > > > > 
> > > > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > > > > > > index b53446bb8c6b..6f4a32df90f6 100644
> > > > > > > --- a/drivers/iommu/iommu.c
> > > > > > > +++ b/drivers/iommu/iommu.c
> > > > > > > @@ -253,8 +253,10 @@ int iommu_probe_device(struct device *dev)
> > > > > > >             goto err_out;
> > > > > > >           group = iommu_group_get(dev);
> > > > > > > -    if (!group)
> > > > > > > +    if (!group) {
> > > > > > > +        ret = -ENODEV;
> > > > > > Can you please explain why you use -ENODEV here?
> > > > > Before 79659190ee97 ("iommu: Don't take group reference in
> > > > > iommu_alloc_default_domain()"), in
> > > > > 
> > > > > iommu_alloc_default_domain(), if group is NULL, it will return -ENODEV.
> > > > Hmm. While I think the patch is ok, I'm not sure it qualifies as a fix.
> > > > Has iommu_probe_device() ever propagated this error? The commit you
> > > > identify in the 'Fixes:' tag doesn't seem to change this afaict.
> > > I think after this commit 439945e74a4b ("iommu: Move default domain
> > > allocation to iommu_probe_device()"),
> > That SHA doesn't exist in my tree (maybe you mean 6e1aa2049154?). But even
> > then, I'm not sure 6e1aa2049154 is actually broken if you look at the
> > interaction with group creation in __iommu_probe_device().
> > 
> > In fact, isn't that the case in mainline too? If __iommu_probe_device()
> > returns 0, then we _know_ a group exists and so iommu_group_get() will
> > succeed. I'm still happy with the patch in case this changes in future,
> > but it doesn't appear to be fixing anything. Do you agree?
> 
> Yes, I look into the __iommu_probe_device(), if it can't get group, it will
> return error
> 
> first.  Do I need send a v2 without the fix tag ?

Yes, I think that would be fine, and perhaps update the commit message
to make it clear that this is purely cosmetic.

Will